Protective system



Sept. 1, 1936.

s. WIDMER ET AL 2, 52,814

PROTECT IVE SYSTEM Filed Dec. 8, 1933 lllillll Patented Sept. 1, 1936 UNITED STATES PROTECTIVE SYSTEM Stefan Widmer and Max Hiirlimann, Baden, Switzerland, assignors to Aktiengesellschaft Brown Boveri & Cie, Baden, Switzerland, a joint-stock company of Switzerland Application December 8, 1933. Serial No. 701,430 In Germany December 15, 1932 '7 Claims.

This invention relatesin general to improvements in protective systems and more particularly to systems for protecting an electron discharge device which supplies an inductive output circuit, against disturbances occurring in the circuit thereof.

It is well known that the current through an electron discharge device energized with alternating current may be prevented upon occurrence of a disturbance by negatively energizing the control electrodes of the device with respect to the associated cathode. If the discharge device is of the vapor type, the flow of current through the anodes of the device is not instantly stopped by the action of the control electrodes, but the control electrodes prevent the several anodes from sequentially picking up current during the voltage cycle of the supply line so that the fiow of current through the device ultimately ceases. To avoid damage to the device resulting from a protracted flow of excessive currents therethrough, such currents should be interrupted in the shortest possible time following their occurrence. If the output circuit of the device is of inductive character, however, the flow of current tends to continue irrespective of the action of the control electrodes until the magnetic energy stored in the inductive portions of the system is dissipated to a substantial extent, continuance of such disturbance causing deterioration or even destruction of the device. By providing means, across the output line, operable to discharge the magnetic energy stored in the output line, the effect of such magnetic energy upon the interrupting operation of the device may be neutralized and the flow of currentmay be interrupted rapidly, thereby avoiding deterioration to the device.

It is, therefore, among the objects of the present invention to provide a protective system for an electron discharge device supplying an inductive output circuit whereby the flow of current is prevented by negative energization of the control electrodes of the device with respect to the cathode potential.

Another object of the present invention is to provide a protective system for an electron discharge device supplying an inductive output circuit in which the magnetic energy stored in the output circuit is discharged in response to the operation of the means energizing the control electrodes.

Another object of the present invention is to provide a protective system for an electron discharge device supplying an inductive output circuit in which the magnetic energy stored in the output circuit of the device may be discharged through means connected across the output circuit line.

Objects and advantages other than those above described will be apparent from the following description when read in connection with the accompanying drawing in which:

Fig. 1 diagrammatically illustrates one embodiment of the present invention in which an electron discharge device operable as an alternating current rectifier supplies current to an inductive direct current line and in which the direct current line is bridged by a discharge path provided within the device; and

Fig. 2 diagrammatically illustrates a portion of a modified embodiment of the present invention in which the direct current line is bridged by energy storage means which may be discharged through the line by means of a relay.

Referring more particularly to the drawing by characters of reference, reference numeral 6 designates an alternating current line constituting the input circuit of the system herein represented as a three phase line. nected with the primary winding 1 of a transformer having a secondary winding 8 comprising a plurality of phase displaced portions connected in star to form a neutral point. The several phase portions of winding 8, such as 8a, are severally connected with the anodes 9 of an electron discharge device of the vapor type having a cathode l2, to be hereinafter referred to as rectifier H for the sake of brevity. Rectifier II is provided with the usual discharge igniting and maintaining means, which do not enter into the operation of the present system and are therefore not shown.

Cathode I2 is connected with one of the conductors l3 of a direct current output line having a second conductor [4 connected with the neutral point of winding 8. Line l3, I4 is assumed to be of inductive character as the result of insertion therein of inductive means such as a current smoothing reactor l6. Rectifier H is provided with a plurality of control electrodes ll severally controlling the operation of anodes 9; during normal operation of rectifier ll, control electrodes I! may simply cooperate with other constructive elements of the rectifier to insure operation thereof free from internal disturbances, or else the control electrodes may be utilized for regulating the flow of current through the rectifier in any well known manner.

Irrespective of the nature of the operation of control electrodes ll, each control electrode is connectible through a resistance as at l8 and the contacts of a relay 2| with the negative terminal of a suitable source of direct current such as a battery l9 having the positive terminal thereof connected with cathode l2. Relay 2| is preferably of the type closing the contacts thereof instantly upon energization of the relay coil and in which the contacts are opened after a prede- Line 6 is contermined time delay following deenergization of the coil. The coil of relay 2| is energized in response to the occurrence of disturbances in the line I3, I4, for instance such coil may be connected across the secondary winding of a current transformer 22 inserted in conductor I3.

For the purpose of discharging the magnetic energy stored in reactor IS, a discharge path is provided directly across the line I3, I4. Such discharge path is preferably constituted by an additional anode 23 of rectifier-II, spaced within the rectifier from cathode I2, but may also be constituted by an electric valve independent of rectifier I I.

In operation, line 6 being energized supplies current to transformer I, 8, such current being rectified in rectifier II and supplied to output line I3, I4 as is well known in the art. Such flow of current is substantially uniform as a result of the presence of reactor I6. During such operation, conductor I4 is negative with respect to conductor I3 and no current can flow between anode 23 and cathode I2 as a result of the valve action of anode 23.

Upon occurrence of a disturbance such as a heavy overload or a short circuit in line I3, I4, a sudden change occurs in the rate of flow of current in conductor I3, thereby causing current transformer 22 to impress a voltage sufiicient to cause operation-of the coil of relay 2I. Battery I9 is thusconnected with control electrodes I1 and impresses, on all control electrodes, a poten-- tial which is negative with respect to the potential of cathode I2. All the anodes 9 not carrying current at the instant considered, are thereby made inoperative (as is well known) and the flow of current cannot be transferred thereto from the anodes then in operation.

The particular anode, 9a for instance, carrying current at the instant considered, is, however, not affected by the energization of the associated control electrode and continues to carry current; In the absence of reactor I3, such fiow of current would continue until the voltage of winding portion 8a supplying current to anode 9a became negative, at which time such current would tend to reverse, and would cease as a result of the valve action of rectifier II.

As a result of the presence of reactor Hi, however, when the voltage of winding portion 8a decreases previous to the reversal thereof, the flow of current tends to be maintained uniform by the appearance of a unidirectional voltage across the terminals of reactor I6. Such voltage tends to maintain anode 9a positive with respect to cathode I2 for a period of time depending upon the inductance of the reactor, thereby delaying the passage of the current through anode 9a through zero and the blocking operation of control electrode I'Ia. When the voltage of winding portion 8a becomes negative, anode 23 is thereby brought to a potential higher than the potential of anode 9a and the flow of current will then occur from conductor I4 to anode 23 to cathode I2, conductor I3 and the load connected with line I3, I4 (not shown) and through conductor I4 to reactor IS. The flow of current through anode 9a is thus momentarily interrupted and control electrode IIa regains control to prevent further flow of current from being reestablished through anode 9a; The fiow of current through line I3, I4 from the rectifier I I supplied from line 6 is thus completely interrupted and line I3, I 4 only carries a decaying current completing the discharge of the magnetic energy stored in reactor I6 through anode. 23 and cathode I2. Such current thereafter ceases and, after a predetermined time delay, relay 2| opens the contacts thereof, thereby causing the blocking action of control electrodes I! to be discontinued, and rectifier II is again operable to function in a normal manner thereof.

From the above description of the operation of the system, it is apparent that control electrodes neutralize the action of the reactor on the operation of. rectifier II.. The operation of relay 2| and current transformer 22 occurs in response to the magnitude of the rate of change of the flow of current in line I3, I 4.

In the embodiment illustrated in Fig. 2, anode 23 is omitted and line I3, I4 is then bridged by a capacitor 24 in series with a resistor 26 of high ohmic value. Resistor 26 may be short circuited by a. relay controlled by additional contacts 28 of relay 2 I.

The normal operation of rectifier I I is the same in the embodiment illustrated in Fig. l and in the present embodiment. pacitor 24 is slowly'charged at the voltage of line I3, I4 through resistor 26 and thereafter remains in. the charged condition.

Upon occurrence of an overload or of a short circuit in line I3, I4, relay 2| closes the contacts thereof, thereby negatively energizing control electrodes I1 and causing operation of relay 21.

. Thefiow of current through rectifier II is then again confined to a single anode such as anode 9a. Upon operation of relay 21, capacitor 24 suddenly discharges through conductor I3, the load connected across line I3, I4, conductor I4 and reactor I6. During such discharge, the voltage of capacitor 24 momentarily brings cathode I2 to a potential higher than the potential of anode 9a and the flow of current through anode 9a therefore ceases, thereby permitting control electrode I'Ia to regain control. When capacitor 24 is completely discharged, the magnetic energy stored in reactor I6 is dissipated in causing recharging of capacitor 24 at a polarity opposite to the normal polarity thereof; such charge is thereafter dissipated through the line and. the load circuit as above described. The system is again put into condition for normal operation by reopening of relays 2| and 27 after a predetermined time delay.

To protect rectifier II against damage, it is of course necessary that the flow of excessive current therethrough be interrupted in the shortest possible time. If, however, relays 2I and 21 were to operate simultaneously, the operation of capacitor 24 in raising the voltage of cathode I2 above that of anode 9a would be opposed by e the positive voltage of winding 8a. The fiow of current through winding So would then be interrupted only when the voltage of winding portion 8a became smaller than the voltage of capacitor 24. As the capacitor begins to discharge immediately upon closure of relay 21, the voltage of a capacitor might then decrease so rapidly that the voltage of winding portion So would remain greater than such voltage and anode 9a would continue to carry current until the magnetic energy of reactor I6 has become substantially During such operation, ca-

dissipated therethrough. It is, therefore, preferable to cause operation of relay 2'! to close the contact thereof when the voltage of winding portion 8a is approximately zero. In rectifiers supplied with current at a large number of phases as in the present instance, relay 21 should close the contacts thereof approximately one-quarter of a cycle after connection of battery I9 with control electrodes I'I. At such instant the flow of current through anode 9a is maintained entirely by the voltage appearing at the terminals of reactor [6 and the flow of current will occur through capacitor 24, which is still charged at full voltage, rather than through the circuit comprising winding portion 8a, anode 9a and cathode l2, in which circuit no electromotive force is then impressed. Capacitor 24 and resistor 26 therefore constitute means connected across lines l3, l4 and responsive to the operation of relay 24 to cause discharge of the magnetic energy stored in reactor I6 to thereby neutralize the action of reactor l6 upon the interrupting operation of rectifier H.

Although but two embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In combination, an alternating current supply line, a transformer connected with said line, an electron discharge device connected with said transformer and having an anode associated with a control electrode and a cathode, a direct current output line connected with said discharge device and with said transformer, inductance means in said output line, means for impressing potential on said control electrode negative with respect to the potential of said cathode, and means connected across said output line and operable to neutralize the action of said inductive means upon operation of the last said means.

2. In combination, an alternating current supply line, a transformer connected with said line, an electron discharge device connected with said transformer and having an anode associated with a control electrode and a cathode, a direct current output line connected with said discharge device and with said transformer, inductance means in said output line, means responsive to abnormal conditions in said output line for impressing potential on said control electrode negative with respect to the potential of said cathode, and means connected across said output line and operable to neutralize the action of said inductive means upon operation of the last said means.

3. In combination, an alternating current sup ply line, a transformer connected with said line, an electron discharge device connected with said transformer and having an anode associated with a control electrode and a cathode, a direct current output line connected with said discharge device and with said transformer, inductance means in said output line, means responsive to the rate of change of the flow of current in said output line for impressing potential on said control electrode negative with respect to the potential of said cathode, and electron discharge means connected across said output line and operable upon operation of the second said means to discharge the magnetic energy stored in said inductance means.

4. In combination, an alternating current supply line, a transformer connected with said line, an electron discharge device connected with said transformer and having an anode associated with a control electrode and a cathode, a direct current output line connected with said discharge device and with said transformer, inductance means in said output line, means responsive to the rate of change of the flow of current in said output line for impressing potential on said control electrode negative with respect to the potential of said cathode, a capacitor connected with one conductor of said output line, a resistor connected with said capacitor and with the other conductor of said output line, and means controlled by the second said means for short circuiting said resistor to thereby cause discharge of the magnetic energy stored in said inductance means.

5. The combination with an electric circuit having a reactance included therein, and an electron discharge device having an anode and a cathode constituting spaced electrodes for the flow of current therethrough to said circuit, of means for controlling said flow of current comprising a control electrode constituting an element of said device, means for impressing potential on said control electrode of such sign and magnitude as to prevent the initiation of said flow of current, and means comprising an element of said device, other than said electrodes, connected with said circuit and constituting an electrode for the discharge of said reactance through said device.

6. The combination with an electric current supply circuit, a work circuit having a reactance included therein, and an electron discharge device having a main anode and a cathode interconnecting said circuits and constituting spaced electrodes for the flow of current through said device from said supply circuit to said work cir cuit, of means for controlling said flow of current comprising a control electrode constituting an element of said device, means for impressing on said control electrode potential of such sign and magnitude as to prevent initiation of said flow of current, and means comprising an auxiliary anode connected with said work circuit and constituting with said cathode spaced electrodes for the discharge of said reactance through said device.

'7. The combination with an electric current circuit having a reactance included therein, and an electron discharge device having an anode and a cathode constituting spaced electrodes for the flow of current therethrough to said circuit, of means for controlling said flow of current comprising a control electrode constituting an element of said device, a source of current for exciting said control electrode in such sense as to thereby prevent the initiation of said flow of current, means operable responsive to an abnormal condition in said circuit for effecting the connection of said source with said control electrode, means having connection with said circuit and operable responsive to operation of the second said means to form a path for the discharge of said reactance.

STEFAN WIDMER. MAX HURLIMANN. 

